In the prior art, a general back (back moving) spring of a control valve of a flush device in a toilet is a common cylindrical compression spring having a circular-section, and which is mounted between a valve cover and a valve piece for the position-restoring act only. Meanwhile, the discharge hole of the valve piece in the control valve is very small. The discharge hole is difficult to make and is also often jammed by impurities, so it needs an additional cleaning device that is also difficult to position into the discharge hole.
As shown as FIG. 1, a back spring 92 is set in a valve core 9 to overcome the above-mentioned defects in the prior arts. It is mounted between a valve cover 91 and a valve piece 93. A valve core body 94 is around the outside of the valve cover 91 and the valve piece 93. The back spring 92 has a cylindrical frame. At one end of this cylindrical compression spring, the steel wire bends outward for a distance in the direction parallel to the diameter of the spring, and then bends by 90 degrees along the direction towards the other end of the back spring 92 to form a pin 95 parallel to the axial line of the back spring 92. During operation, the pin goes through a discharge hole 96 of the valve piece 93. The pin 95 is so mounted that it may be positioned in the discharge hole. When the valve piece 93 is moving, the pin 95 can clean out any impurities in time to avoid a jam. Meanwhile, the discharge hole 96 may be larger due to the existence of the pin 95, which may allow the discharge hole 96 to be processed easily. But the back spring of this flush control valve still has the defects that it is not easily positioned into the discharge hole and its size is still too big.
In the prior art, in the process of accommodating and using the pin and back spring of the valve core, it is difficult to correctly keep the pin positioned into the discharge hole of the valve core. Thus, the pin may easily be bent out of shape during use and lose its function. Moreover, the pin is easily lost in the process of maintenance to the flush control valve core.
Therefore, it is necessary to provide a flush control valve having a back spring which has a reliable structure and can be held steadily within the valve core body.